Home » Target Disease

Colorectal Cancer

What is it? Who gets it?

Cancer of the colon and rectum is the third most commonly occurring cancer in Canada and the United States and the second leading cause of cancer death. The American Cancer Society estimates that about 150,000 new cases of colorectal cancer will be diagnosed in 2006, and about 60,000 people will die of the disease.1

Colorectal cancer begins in the cells and tissues lining the colon, a muscular tube about five feet long that connects the small intestine to the anus (the rectum is the last few inches of the tube). Colorectal cancer almost always develops first in small growths called polyps or adenomas, and it can take decades for polyps to develop into cancer. Detection of precancerous lesions is an opportunity for physicians to remove them before they develop into cancer.

  • Most adenomas never develop into cancer; however, most cancers start as adenomas.
  • About 40% of people age 50 have adenomas; however only about 2% of these ever become cancerous.2
The earlier colon cancer is detected, the better chance of survival:
  • The 5-year relative survival rate for people whose colorectal cancer is treated in an early stage is better than 90%
  • The 5-year relative survival rate if cancer has spread to distant organs (i.e., the liver or lung) is less than 10%
  • Only 40% of colorectal cancers are found in early treatable stages.1

For these reasons, health authorities such as the US Preventive Services Task Force, the American Cancer Society and the Canadian Cancer Society urge all adults to consult with their doctors about regular screening for colorectal cancer starting at the age of fifty.1,3,4 Below that age there is little risk of sporadic colon cancer although some, more rare forms of colon cancer have a heritable component and can strike earlier.7

Why don't people get screened for colorectal cancer?

US President Ronald Reagan’s 1985 surgery for colon cancer was responsible for increasing public awareness of colorectal cancer. In 2000, NBC’s Today Show host Katie Couric – who lost her husband to colon cancer in 1997 - had her own colonoscopy televised in order to promote colorectal cancer screening. For years experts have promoted the message that screening healthy adults saves lives: the American Cancer Society estimates that the death rate from colon cancer could be halved, from 60,000 deaths per year to 30,000 if Americans would undergo regular colorectal screening.5

Despite recommendations and the publicity generated by high profile cases, however, few North Americans are screened for colon and rectal cancer. Fewer than 50% of North Americans undergo the recommended tests for the early detection of colon and rectal cancer.6

One reason for the low number of colorectal screens performed, despite the fact that screening saves lives, is that today’s screening tests for colorectal cancer are not perfect and not without their drawbacks. The “gold standard” test for colon and rectal cancer is colonoscopy, an examination that uses a long endoscope with an attached camera lens to visualize the entire colon for polyps and early cancers. During the examination, small lesions can be removed and larger lesions can be biopsied for examination by a pathologist. Colonoscopy is considered a highly effective screening tool for cancer.3

Colonoscopy is considered a highly effective screening tool for cancer. But there are drawbacks.3

  • Colonoscopy is inconvenient. The patient must take a day off work and be sedated for the procedure. Preparation includes a change in diet for up to a week before the exam as well as an uncomfortable process to evacuate the bowels. Incomplete preparation can result in the need to repeat the test.
  • Complete colon visualization is a challenging procedure even for experts and there are risks, including a small risk of bowel perforations (about 3 per 1,000 tests) or bleeding (less than three per cent)
  • Colonoscopy is expensive, with costs ranging from US $800 to $1200 per test.
  • Most colonoscopies return negative findings and so a better screening test may reduce the need for expensive, cumbersome colonoscopy. At the same time, screening for those who likely do have lesions that should be biopsied or removed is an effective way to enhance the utility and effectiveness of colonoscopy.

References

  1. American Cancer Society. Detailed Guide: Colon and Rectum Cancer.
  2. Burke CA. Colorectal Neoplasia. 2009. Cleveland Clinic.
  3. Canadian Cancer Society. Screening for Colorectal Cancer.
  4. US Preventative Services Task Force. 2002. Screening for Colorectal Cancer.
  5. American Cancer Society. What you need to know about colon testing.
  6. Weitz J et al. Colorectal Cancer. Lancet. 2005; 365: 153-165
  7. Genetic Health. What is HNPCC?